Waste water treatment

ABSTRACT

A process for facilitating the separation of fat from a waste stream composition comprising water, fat, fatty acids and solids produced in food processing plants and animal rendering plants. In one embodiment, an alkaline pH control composition and an aluminum salt flocculant composition are added to the waste stream composition for subsequent separation in a clarifier of the waste stream composition into an essentially fatty layer, an essentially water layer, and an essentially solids layer. In a second embodiment, a conventional dissolved air flotation system is employed. An acidified aluminum salt flocculant composition is added to the waste stream composition prior to dissolved air introduction. The resulting waste stream composition subsequently separates in a clarifier into the three layers described above.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation-in-Part of copending application Ser.No. 850,580 filed Apr. 11, 1986.

BACKGROUND OF THE INVENTION

This invention relates to the field of fat rendering and moreparticularly to methods and compositions for improving the separation ofinedible fat from process water and solid waste.

Fat rendering facilities have conventionally employed several methodsfor separating water from inedible fats and solids in the processing ofwaste resulting from the rendering operation, after the removal of themelted edible fat. In currently employed processes the waste, afterseparation of edible fat, includes inedible fat, water, and solids. Mostrendering facilities use some type of holding tank or clarifier. Some ofthese clarifiers, or holding cells, use skimmer technology to remove fatand solids from several waste water streams throughout a typical plant.All these waste streams are brought together into such a holding cell.These waste streams co-mingle in the holding cells and tend, after timeto roughly separate into three distinct layers or phases. The top-mostlayer contains largely fat or grease, together with water and some freefatty acids and salts of free fatty acids. The middle, and by far thelargest phase, is the water layer generated from the water used in theprocess. This layer will also contain most of the same materials foundin the top layer in different proportions. Finally, solids or sludgerepresents the bottom layer.

There are two primary purposes of these holding cells. First, removal ofthe fat and inedible tallow which, after a sufficient period of timerises to the surface where it can be removed by skimming which can thenbe sold. Secondly, it is necessary to perform the separation efficientlyin order to discharge the waste water at an acceptable level of purity.Normally, if the retention time of the holding cell is long enough, thenthe separation of these three phases is improved to an acceptable level.This can and has been accomplished by increasing the capacity of theholding cells. This has, in the past, been the most used method ofincreasing the retention time.

In most holding cells or clarifiers, the subsequently separated fatlayer, water layer and sludge layer are characterized, individually,with respect to the respective disposition of each layer. For example,the quality of water (middle phase) is generally measured by itsBiological Oxygen Demand (B.O.D.) and the Suspended Solids (S.S.) in thewater. The measured B.O.D. values and S.S. values (usually expressed inweight per unit volume, i.e. mg/l) are used to determine theacceptability and cost of discharge. For most water discharges (riverand sewer), the cost to discharge the effluent is, among other things,also dependent upon the quantity of water; however, this is essentiallyconstant from day to day when the processing or rendering plant isoperating. Other measurements and restrictions are used occasionally indetermining the quality of water depending on the local municipalitiessuch as temperature, chemical oxygen demand (C.O.D.), or ammoniacontent. Generally, if one lowers either the B.O.D. or S.S. of thewater, then the charge for discharging the water would be reduced. It isnot economically feasible at the present time for some industries,including fat rendering plants, to eliminate the B.O.D. and S.S. valuesin water completely.

The sludge in the bottom layer is usually pumped or augered out of theplant and taken to one of many large lagoons. These discharge lagoonsare alternated in such a fashion that the solids can be air dried anddisposed of in a land fill operation.

The skimmings obtained from the top layer are cooked and sold asinedible tallow. In continuous rendering systems, the tallow can beblended with other fat prior to cooking in a cooker. In a batchrendering operation it may be cooked and sold separately or blended withother fat.

The tallow obtained, i.e. flotation grease, from the holding cells isgenerally of poor quality and represents from 2 to 10 percent of thetotal inedible tallow for a typical beef packing operation. Although,this percentage is small; it influences the quality of the entireinedible tallow considerably if it is blended.

Color and the free fatty acid (FFA) content of the tallow from theskimmings are the two primary criteria used in determining the quality,and therefore, the value of the tallow. There are several othermeasurements that can be used but are less significant. Furthermore,color (F.A.C.) and F.F.A. content correlates to one another. A darkcolor generally means a high F.F.A. content. It is because of thisrelationship that the determination of the F.F.A. is used to evaluatethe value of the skimming or total inedible tallow. Under normaloperating conditions the F.F.A. of flotation grease can vary between 3and 85 percent for most facilities, which when higher than about 4percent is undesirable.

In addition the quality of the water discharged from the holding tanksgenerally contains sufficient soluble impurities and suspended solids torender direct discharge costly or impossible without further treatment.

OBJECT OF THE INVENTION

It is therefore an objective of the present invention to improve theyield of fat from clarifiers used in meat packing and renderingfacilities while lowering the F.F.A. content of the flotation grease,its moisture content, and, to improve the color so that it can beblended or sold separately after cooking to produce a tallow with ahigher economic value and lower capital cost than possible withconventional holding cell or clarifier systems.

It is also an objective of the present invention to provide compositionsand methods for improving the quality of water separated from the sludgeor solids and flotation grease whereby the B.O.D. values of the waterand the suspended solids content are substantially reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a dissolved-air-flotation system forthe treatment of a waste stream produced in an animal fat renderingoperation.

BRIEF SUMMARY OF THE INVENTION

The present invention achieves the hereinbefore stated objectives by theaddition of two separate compositions, in aqueous solution to the wastewater stream, preferably before the stream enters a clarifier-skimmer.In a first embodiment the first composition is a pH control compositioncomprising a combination of a compound or mixture of compounds capableof producing a predetermined pH in a clarifier or holding tank and asurfactant. The second composition, in solution, is a flocculantcomposition, such as aluminum sulfate, alone or in combination with anenzyme such as a protease. These compositions are added to the wastewater stream containing solids and inedible fat in amounts, describedmore fully hereinafter, which are effective to provide an increase infat separated from the waste water which has improved color and lowerFFA than clarifying processes operated without the addition of thesecompositions. In a second embodiment employing a dissolved air flotation(D.A.F.) system, the process comprises the addition to the waste waterstream of a flocculant composition such as that described above prior tointroduction of the dissolved air to the stream, and addition to thewaste water stream of a pH control composition such as that describedabove subsequent to the dissolved air introduction. The waste streamthen enters the clarifier or holding tank for subsequent separation. Theinfluent of the stream at the time of introduction of the flocculantcomposition must be acidic, and such acidity can be achieved byproviding an acidified flocculant solution comprising, for examplealuminum sulfate along with sodium bisulfate, sulfamic acid, or othereffective acid or salt to achieve the required pH value. This wastestream treatment is effective in pork and beef rendering operations, andlikewise yields an increase in fat which has improved color and lowerFFA content than D.A.F. clarifying processes operated without theaddition of the compositions as above described. The processes of thepresent invention utilizing effective amounts of the describedcompositions also provide a reduction in the suspended solids, B.O.D.value, and fat in the separate water layer formed in the clarifier.

DETAILED DESCRIPTION OF THE INVENTION

The waste water effluent from a fat rendering facility normally containsa complex mixture of water, solids and inedible fat.

Further, the natural emulsifiers present in the mixture tend to bothdisperse the fat into the water phase and the water into the fat phase.This natural action of the materials present in the waste water streamseverely complicates the separation of fat from the water, adverselyeffecting both the quality of the water and the quality of the fat.

There are several natural emulsifiers that can disperse fat into thewater phase and visa versa. Low molecular weight proteins are alwayspresent and act as emulsifiers which contribute to the describedundesirable dispersion of fat into water and water into the fat. Theprimary emulsifiers, because of the large quantity present, are thefatty acids and the salts of these fatty acids. Fatty acids are slightlysoluble in water and much more soluble in fat. Whereas, the salts ofthese free fatty acids are generally soluble in water and less solublein the fat phase. In this mixture the fat molecules are more associatedwith the fatty acid molecules, and the water molecules are moreassociated with the salts of the free fatty acids.

The emulsification of the waste water system is very dependent upon thepH of the waste stream. If the pH was very low (i.e. less than about3.0) then the four component system would be reduced to threecomponents. The salt of the free fatty acids would be replaced by freefatty acids. In this case, a pH less than about 3, the only emulsifierwould be fatty acids. This condition leads to a high F.F.A. content inthe flotation grease.

On the other end of the pH scale, i.e., pH's generally greater thanabout 10, the free fatty acids would be neutralized; thus resulting inan increase of salts of free fatty acids, called tallow soaps. Thiswould leave, predominately, only these salts of free fatty acids as theemulsifiers for the fat-water system. This can then create too muchfoaming in the cookers as well as losses in the flotation grease due tohydrolysis.

In most facilities, the pH of the waste streams varies substantiallydepending on the type of waste water stream involved, but is generallyacidic. However, in practice, the pH of the holding cells, orclarifiers, is generally about 7.0±1.5 or near neutral because of thelarge buffering capacity of the cells. Thus, in the vast majority of theplants the true four component system is in operation.

As described, the two emulsifiers described, i.e., fatty acid and thesalts of fatty acids, have good transport properties for water moleculesmigrating into the fat and the fat molecules into the water. Both ofthese properties are undesirable. The water molecules in the fat couldyield more free fatty acids in further processing particularly whenenzymes are present. Lipases occur naturally in the fat tissue ofanimals and are generally present in the waste water recovered from thesystems previously described. The presence of water is necessary tobreak-down the fat molecules into fatty acids and glycerine. Fatmolecules in the water phase would yield higher B.O.D. and S.S. valuesof the water.

As previously mentioned, the fat molecules are more associated with thefatty acids. In fact, one can picture a fat molecule surrounded by fattyacid and/or derived salts of fat molecules in the water phase. Theopposite of this is also true, the water molecules would be surroundedby the salts of fatty acids and/or fatty acid molecules in the fatphase. Therefore, according to the objectives and teachings of thepresent invention it is considered important to break-up theseassociations in order to provide for better separation. A better tallowwould result and the quality of water would be improved.

Treatment of the waste water according to the present invention can be atwo step process or a single step process for the first embodimentthereof, and is a two-step process for the second embodiment as earlierdescribed. The process involves many chemical reactions in order tobreak-up the association promoted by the emulsifiers between fat andwater. First, the use of an effective amount of a surfactant isnecessary to penetrate the association. Once the fatty acid is freed bythe surfactant, it is essential to provide for the presence of acomposition in sufficient amounts to be capable of producing in aclarifier, and maintaining during clarifications, a pH of from betweenabout 6.0 to about 6.5 in order to produce free fatty acid salts. Thisis illustrated by the following, representative chemical reaction:##STR1##

Next, according to the present invention, it is necessary to react thesodium salt of the free fatty acid (NaFA) with aluminum ion which isrepresented as follows:

    3NaFA+Al.sup.+3 →3Na+Al(FA).sub.3

The aluminum fatty acid salt that is formed in the water phase floats tothe top of the typical waste water holding cell treated with thecomposition of the present invention. Aluminum salts of free fatty acidsare greases and are soluble in the fat. Furthermore, there is no waterassociated with this salt unlike the sodium salt or the free fatty aciditself. This mechanism reduces the water content of the fat and also thefat content of the water.

A secondary function for the aluminum ion addition is the formation of aprecipitating flocculant that traps suspended solids and otherimpurities in the water system.

Optionally, by adding an enzyme to the system that consumes proteins,one can break the protein induced emulsification of fat into the waterphase and water into fat layer. Incorporation into the chemical additionof such an enzyme further assists the de-emulsification process. Thisenzyme addition also aids in destroying the lipase that produces fattyacids and glycerine from fat.

The pH control composition of the present invention comprises an aqueoussolution of a compound or mixture of compounds in sufficient amounts tobe capable of producing the desired pH in a clarifier, and about 0.1% toabout 5% by weight of a surfactant. The pH controlling component used inthe present invention can be selected from the group consisting ofsodium hydroxide, potassium hydroxide, lithium hydroxide, magnesiumhydroxide, calcium hydroxide, sodium carbonate, potassium carbonate,lithium carbonate, sodium metasilicate, potassium silicate, sodiumphosphates, potassium phosphates, ammonium hydroxide, and any mixturesthereof which will produce the described pH. The pH controllingcomponent of the present invention is preferably used in the pH controlcomposition in amounts equivalent to 20% to 50% by weight of sodiumhydroxide in the solution.

One preferred combination of pH controlling component in the controlcomposition is a combination of sodium and potassium hydroxide whichprovides an equivalent alkalinity in the solution of about 35% by weight(expressed as NaOH) and can reduce the freezing point of the solutionsufficiently to enable the use of the solution in waste water clarifierswhich are open to a cold winter environment. This concentration producesthe advantage described when used in packing plants in amounts of fromabout 3.5 to 70 parts per million (ppm) of the waste water. Preferably,the pH control composition is utilized in amounts of from about 10 toabout 30 ppm and most preferably in amounts of from about 15 to 20 ppm.

Where the invention is practiced in a rendering facility, the pH controlcomposition can be used in amounts of from about 7 to about 175 ppm, andmore preferably in amounts of from about 30 to about 70 ppm and mostpreferably in amounts of from about 45 ppm to about 55 ppm.

The surfactant selected is preferably a non-ionic alkyl glucoside suchas Triton BG-10 supplied by Rohm & Haas Co. of Philadelphia. Othersurfactants capable of functioning as described, such as aliphaticorganic phosphate esters and salts of dicarboxyethyl fatty acid derivedimidazoline can also be employed. Such materials are readily obtainableand other surfactants can be employed without undue experimentation todetermine the effective amounts in the systems described.

The preferred flocculant composition comprising aluminum sulfate in anaqueous solution is used in packing plants in amounts of from about 5 toabout 30 ppm and more preferably 10 to 20 ppm. In rendering facilities,the solution can be used in amounts of from about 10 to 100 ppm, andpreferably in amounts of from about 20 to about 60 ppm and mostpreferably in amounts of from about 30 to about 40 ppm.

The flocculant composition can also advantageously contain a minoramount of a protease. In the embodiments described, Neutrase 1.5T enzymeobtained from Novo Laboratories, Inc. of Wilton, Conn., was used.

The following Example and Tables describe how the present invention canbe used effectively in processing and rendering plants.

EXAMPLE 1

The present invention has utility for improving the function ofclarifiers used for separating fat and suspended solids. Typically,clarifiers are used in rendering plants and meat packing plants. In thisexample, the compositions and methods of the first embodiment of thepresent invention (non-D.A.F. system) were used in a beef packingfacility processing about 3000 head of fat cattle in an eight hour day.This plant uses between about 1.6 million and 1.8 million gallons ofwater per day, and produces up to about 250,000 pounds of inedibletallow per day. The waste water treatment portion of this facilityemploys three clarifiers to remove the fat and sludge from the combinedwaste water streams. In this particular plant, two of the clarifiers arein parallel to each other and are used as secondary clarifiers for thelower fat content water effluent from the primary clarifier. Thefunction of the primary clarifier is to permit separation of solids andfat from the combined waste water stream and to skim about 95% of thewaste fat from the waste water. All of the waste water from processingstations throughout the plant are pumped into the primary clarifier andthen after primary separation of the fat and solids from the water, thewater is then pumped to the secondary clarifiers for further removal offat from the water. The skimmed fat from the primary and secondaryclarifiers is then mixed with the other inedible tallow obtained fromprocessing before cooking or to processed tallow after cooking.

The inedible tallows obtained from the skimmings are generally between5% to 10% by weight of the total tallow production and is generally ofpoor quality having an FFA number greater than 17. This fat, when mixedwith the other process derived fat tends to lower the overall quality ofthe final tallow product.

During the processing described, an aqueous solution of pH controlcomposition (composition No. 7 in Table II) was added to the waste waterentering the primary clarifier at a rate of 30 gallons in a twenty fourhour period. At the same time an aqueous flocculant solution comprisingaluminum sulfate was introduced into the waste water. In an eight hourperiod, typically about 200 pounds of the aluminum sulfate, dissolved in110 gallons of water was used. Preferably the flocculant solution wasintroduced into a waste water surge tank or pit prior to the waste waterbeing pumped into the primary clarifier. The resulting waste streamcomposition was held in the clarifier for a period of time sufficient toeffectuate formation of the three layers previously described. Thisco-administration of the two solutions, containing the compositions ofthe present invention, in aqueous solutions, produced the followingresults in Table I:

                  TABLE I                                                         ______________________________________                                                       Control  Treatment                                             ______________________________________                                        Kill/8 hour day  3,000      3,000                                             Inedible Tallow lbs/day                                                                        250,000    258,000                                           FFA in processed tallow                                                                        2.8%       1.5%                                              FFA in skimmings 17%        about 2%                                          BOD Waste Water             30% less than                                                                 control                                           SS in Waste Water           30% less than                                                                 control                                           ______________________________________                                    

The results described in Example 1 are representative of the kinds ofresults that can be obtained in an increase in the fat obtained in thefat layer and a reduction of free fatty acids in the fat layer, thereduction in B.O.D. and suspended solids in the exit water from theclarifier.

Typical compositions useful in the process of the present invention areshown in Tables II and III: The line numbers in each table represent thesame example for purposes of comparison between results obtained.

                  TABLE II                                                        ______________________________________                                        Aqueous Solutions of Caustic and Surfactant                                                                Equivalent                                       Caustic Part    Surfactant** Alkalinity*                                      ______________________________________                                        (1)    50% NaOH     5% T-10      50%                                          (2)    50% NaOH     5% T-10      50%                                          (3)    50% NaOH     0.5% T-10    50%                                          (4)    50% NaOH     0.5% T-10    50%                                          (5)    40% NaOH     3% T-10      40%                                          (6)    40% NaOH     0.3% T-10    40%                                          (7)    35% NaOH     0.2% T-10    35%                                          (8)    35% NaOH     5% T-10      35%                                          (9)    45% KOH      0.2% T-10    32.1%                                        (10)   45% KOH      2.0% T-10    32.1%                                        (11)   45% KOH      0.5% B-H     32.1%                                        (12)   45% KOH      2.0% B-H     32.1%                                        (13)   28.5% NaOH   0.3% T-10    34.9%                                               9% KOH                                                                 (14)   28.5% NaOH   3% T-10      34.9%                                               9% KOH                                                                 (15)   28.5% NaOH   0.2% T-10    34.9%                                               9% KOH                                                                 (16)   28.5% NaOH   2% T-10      34.9%                                               9% KOH                                                                 (17)   18.5% NaOH   0.2% T-10    34.9%                                               23% KOH                                                                (18)   18.5% NaOH   2% T-10      34.9%                                               23% KOH                                                                (19)   30% NaOH     0.3% B-H     30%                                          (20)   25% NaOH     0.3% B-H     25%                                          (21)   25% NaOH     1.0% CEM     25%                                          (22)   25% NaOH     1.0% CEM     25%                                          (23)   25% NaOH     0.2% Bi      25%                                          (24)   25% NaOH     0.2% Bi      25%                                          (25)   30% KOH      0.2% T-10    21.4%                                        (26)   30% KOH      0.2% Bi      21.4%                                        (27)   30% KOH      0.2% CEM     21.4%                                        (28)   30% KOH      0.2% B-H     21.4%                                        (29)   30% KOH      2.0% T-10    21.4%                                        (30)   30% KOH      2.0% Bi      21.4%                                        (31)   30% KOH      2.0% BH      21.4%                                        (32)   30% KOH      2.0% CEM     21.4%                                        (33)   20% NaOH     0.2% Bi      20%                                          (34)   20% NaOH     2% Bi        20%                                          (35)   20% NaOH     0.2% BH      20%                                          (36)   20% NaOH     2% BH        20%                                          (37)   20% NaOH     0.2% CEM     20%                                          (38)   20% NaOH     2% CEM       20%                                          (39)   20% NaOH     0.2% T-10    20%                                          (40)   20% NaOH     2% T-10      20%                                          ______________________________________                                         *Based on sodium hydroxide (100%)                                             **T10: Triton BG10                                                            CEM: Monateric CEM 38                                                         BH: GAFAC650                                                                  Bi: GAFAC BI750 or BI729 phosphate esters                                

                  TABLE III                                                       ______________________________________                                        Product B                                                                     Powder Mixture                                                                       Hydrated                                                                      Aluminum Sulfate                                                                             Enzyme*                                                 ______________________________________                                        (1)      99.95%           0.05% N-1.5                                         (2)      99.5%            0.5% N-1.5                                          (3)      99.95%           0.05% N-1.5                                         (4)      99.5%            0.5% N-1.5                                          (5)      99.9%            0.1% N-1.5                                          (6)      99.5%            0.5% N-1.5                                          (7)      99.9%            0.1% N-1.5                                          (8)      99%              1.0% N-1.5                                          (9)      99.9%            0.1% N-1.5                                          (10)     99.5%            0.5% N-1.5                                          (11)     99.5%            0.5% N-1.5                                          (12)     99.9%            0.1% N-1.5                                          (13)     99.9%            0.1% N-1.5                                          (14)     99.9%            0.1% N-1.5                                          (15)     99.4%            0.6% N-1.5                                          (16)     99.4%            0.6% N-1.5                                          (17)     99.9%            0.1% N-1.5                                          (18)     99.4%            0.6% N-1.5                                          (19)     99.0%            1.0% N-1.5                                          (20)     99.4%            0.6% N-1.5                                          (21)     99.95%           0.05% N-1.5                                         (22)     99.4%            0.6% N-1.5                                          (23)     99.95%           0.05% N-1.5                                         (24)     99.4%            0.6% N-1.5                                          (25)     99.4%            0.6% N-1.5                                          (26)     99.4%            0.6% N-1.5                                          (27)     99.4%            0.6% N-1.5                                          (28)     99.4%            0.6% N-1.5                                          (29)     99.4%            0.6% N-1.5                                          (30)     99.4%            0.6% N-1.5                                          (31)     99.4%            0.6% N-1.5                                          (32)     99.4%            0.6% N-1.5                                          (33)     99.4%            0.6% N-1.5                                          (34)     99.4%            0.6% N-1.5                                          (35)     99.95%           0.05% N-1.5                                         (36)     99.95%           0.05% N-1.5                                         (37)     99.4%            0.6% N-1.5                                          (38)     99.4%            0.6% N-1.5                                          (39)     99.95%           0.05% N-1.5                                         (40)     99.95%           0.05% N-1.5                                         ______________________________________                                         *Neutrase 1.5T                                                                Product of NOVO Laboratories, Inc.                                       

EXAMPLE 2

As schematically illustrated in FIG. 1, the second embodiment of thepresent invention employing a D.A.F. system was used in the treatment ofboth beef and pork rendering operations. The D.A.F. system is aconventional system comprising a waste stream line traveling through astandard lift station to a clarifier or holding tank and wherein theline has introduced thereto dissolved air generated by a standard airinjection tank disposed between the lift station and the clarifier. Thewaste stream influent contains a water/fat/suspended solids compositionas earlier described. Upon leaving the lift station and prior to theintroduction of dissolved air, the influent entering the waste streamline has introduced thereto the flocculant composition comprising anaqueous aluminum sulfate flocculant solution as described in Example 1,or as selected from Table III, except that the solution is acidifiedwith an acidifying component such as a mixture of sulfamic acid andsodium bisulfate, or the like, and can include a de-duster, rustinhibitor, and the like. The acidified flocculant composition hereemployed contains, by weight, 87.31% sodium bisulfate, 11.64% aluminumsulfate, 0.64% Hisil 233 de-duster (PPG Industries, Inc., Pittsburgh,Pa.) and 0.41% Rodine 130 rust inhibitor (Amchem Products, Inc., Ambler,Pa.), dissolved in water at a concentration of 100 pounds of compositionper 50 gallons of water. Such addition of the acidified flocculant issuch that the pH of the waste stream is from about 3.5 to about 6.8,preferably from about 4.5 to about 6.0, and most preferably from about5.0 to about 5.4. Dissolved air is then conventionally introduced to thewaste stream so treated. Subsequently, the pH control composition asdescribed in Example 1 or as selected from Table II is introduced to thewaste stream in amounts equivalent to 20% to 50%, preferably about 35%,by weight of sodium hydroxide in the pH control composition and theresulting waste stream enters the clarifier for separation into thethree layers as previously described.

It has been found that the site and sequence of addition of theflocculant composition and the pH control composition are crucial toachieve desired end-product results when a D.A.F. system is employed.While the earlier-described chemical reactions occur to yield aluminumsalts of free fatty acids, introduction of dissolved air requires thewaste stream to first contain the flocculant composition and have a pHvalue as earlier related. It is believed that the introduction ofambient air into the waste stream increases acidity through theproduction of carbonic acid from carbon dioxide in such ambient air. Ifthe alkaline pH control composition were present at the time of such airintroduction, a portion of the alkalinity of the pH control compositionwould be lost through neutralization by the carbonic acid to therebyreduce effectiveness. Conversely, addition of the pH control compositionsubsequent to air introduction permits effective pH control within theclarifier.

Employment of a D.A.F. system as above described is useful for both beefand pork rendering operations. For beef, 1.2 pounds of flocculantcomposition per 10,000 gallons of waste stream water and one gallon ofpH control composition per 100 head beef (fat cattle) or 1.25 gallonsper 100 head cow kill provides the desired increases in the fat obtainedand decrease in free fatty acids in the fat layer, and a reduction ofB.O.D. value and suspended solids in the exit water from the clarifier.In the treatment of pork, 1.6 pounds of flocculant composition per10,000 gallons of waste stream water and one gallon of pH controlcomposition per 800 head butcher hogs or 1.5 gallons per 800 head boarsand sows provides the same desired results as for beef.

While illustrative and preferred embodiments of the invention have beendescribed, it is contemplated that alternative embodiments may beemployed to provide objectives and advantages of the invention. Thus, itis intended that the claims be construed to include alternativeembodiments except insofar as limited by the prior art.

What is claimed is:
 1. A process for facilitating the separation of fatfrom a waste stream composition comprising water, fat, fatty acids, andsolids produced in food processing plants and animal rendering plants,said process comprising in sequence:(a) adding a flocculant compositionto the waste stream compostion, said flocculant composition comprisingan aluminum salt in a quantity sufficient to subsequently react withsalts of fatty acids subsequently produced to yield aluminum saltsthereof, and further comprising an acid component sufficient to impart apH value of from about 3.5 to about 6.8 to the waste stream composition;(b) injecting air into the resulting waste stream composition of (a);(c) adding an alkaline pH control composition to the resulting wastestream composition of (b), said pH control composition comprising a pHcontrol component having an equivalent alkalinity of from about 20% toabout 50% by weight of sodium hydroxide to produce a pH of from about6.0 to about 6.5 in the resulting waste stream composition to yieldsalts of the fatty acids in the original waste stream composition, saidsalts reacting with the aluminum salt of (a) to produce said aluminumsalts, and further comprising a surfactant in an amount of from about0.1% to about 5% by weight of the pH control composition; and (d)holding the resulting waste stream composition of (c) in a clarifier fora period of time sufficient to effect separation of said compositioninto three layers, the bottom layer thereof comprising essentiallysolids, the middle layer thereof comprising essentially water, and thetop layer thereof comprising essentially fat which can be recovered byskimming for further processing.
 2. The process of claim 1 wherein thealuminum salt is aluminum sulfate.
 3. The process of claims 1 or 2 andwherein the flocculant composition contains a protease.
 4. The processof claim 1 wherein the pH value imparted to the waste stream compositionis from about 4.5 to about 6.0.
 5. The process of claim 4 wherein the pHvalue imparted to the waste stream composition is from about 5.0 toabout 5.4.
 6. The process of claim 1 wherein the pH control component isselected from the group consisting of sodium hydroxide, potassiumhydroxide, and mixtures thereof.
 7. The process of claim 1 wherein theacidic component of the flocculant composition is selected from thegroup consisting of sodium bisulfate, sulfamic acid, and mixturesthereof.